De Gennes factor

Fig. 8. Critical temperatures for superconductivity, Tc, and for antiferromagnetic ordering, Tn, for RNijI C compounds with R = Lu, Tm, Er, Ho, Dy, Tb and Gd. DG is the de Gennes factor, g the Land factor and J the total angular momentum of the /t3+ Hund s rule ground stale. The straight lines represent rough linear...

Fig. 62. Dependence of the superconducting transition temperature Tc on the effective de Gennes factor DG for the non-magnetic superconductors (a) YNiiBiC and (b) LuNijBjC, both diluted by the magnetic rare earth elements Ho. Dy, Gd. The solid line in (a) corresponds to the theory of Abrikosov and Gor kov (1961).

FIGURE 17 The experimental values ( ) and calculated values of the Curie-Weiss temperature 0 scaled with the de Gennes factor ( ) and gj/x /(/ + 1) (A) which are then normalized to the experimental value of TbB44Si2- Data for RB44Si2 with R = Tb, Dy, Ho, Er, Tm, Yb were obtained for FZ grown crystals while Gd data was obtained for arc melted GdB44Si2 polycrystalline samples (Mori, 2006a). 

Here Ni and N2 are the numbers of Fe and R atoms per mole, respectively gi and g2 are the corresponding Lande factors G - is de Gennes factor hn, h22 and h21 -effective exchange fields, Si is spin of Fe ions, Z22 is the number of R neighbors of each R atom, A22 - is the exchange interaction integral of R atom with R neighbors. 

The obvious merit of Eq. (9) is the explicit dependence of the Curie temperature on the de Gennes factor and the possibility to estimate the exchange field h2 from the Fe sublattice acting on the rare-earth ions. 

Fig. 16. The dependence of on the de Gennes factor (g -1) xJ(J + l) of some heavy RAI2 compounds. ( Van Daal et al., 1969a Gratz et al., 1981a).

Since the B-C bonds in RB2C2 do not require any electron transfer from rare earth metals, all the rare earth diborodicarbides are expected to have three conduction electrons per formula unit. Therefore, it is reasonable to assume that the main magnetic interaction in RB2C2 is the f-f indirect exchange via conduction electrons (the RKKY interaction), as was subsequently verified by the relation of the values with the de Gennes factors (Sakai et al. 1982a). 

Fig. 7.4. Interlayer turn angle data vs. the de Gennes factor for the heavy lanthanide metals and binary alloys as determined from single crystal neutron diffraction experiments. o>i is the initial turn angle (just below Tn) [after Koehler (1972)]. Legend pure rare earth elements A Er-Dy alloys Er-Tb alloys V Er-Gd alloys O Ho-Dy alloys A Ho-Tb alloys.

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